AssessmentsAnatomy and physiology of the male reproductive system
Anatomy and physiology of the male reproductive system
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 50-year-old man comes to the emergency department because of injuries after falling off a ladder. He describes falling about 5 feet off the ground and suffering blunt trauma to his perineum and penis, resulting in immediate pain lasting 5 minutes. Following the injury, the patient experienced burning with urination and noted large amounts of hematuria. He denies pain with ambulation and does not recall any trauma to the pelvis during the fall. Genitourinary examination reveals blood at the urethral meatus. Which of the following is the most appropriate initial step in management?
Content Reviewers:Rishi Desai, MD, MPH
The male reproductive system includes internal and external organs and structures that help with reproduction.
The testes themselves are covered on the outside by the tunica albuginea - a white, fibrous layer.
The seminiferous tubules come together and form a single straight tubule that exits the lobule, and enters a small network of tubules called the rete testis.
A seminiferous tubule has a thick wall of epithelial cells that surround a fluid-filled lumen - a bit like a garden hose.
The wall of the tubule is made up of three kinds of cells: at the periphery, there’s the spermatogonia - which are the primordial sperm cells that begin dividing over and over in puberty, and give rise to male gametes.
Next, there are the spermatocytes - which migrate towards the lumen as they differentiate into sperm.
Finally, there are Sertoli cells - which are large cells that extend from the margin all the way to the lumen of the tubule.
At puberty, secretion of these hormones intensifies and becomes pulsatile - sometimes more of the hormone is released, and sometimes less of the hormone is released.
LH binds to Leydig cells, and stimulates the production of testosterone, whereas FSH binds to Sertoli cells, making them produce androgen binding protein - or ABP, for short - which allows more testosterone to cross the blood-testis barrier and enter the seminiferous tubule.
Spermatogenesis starts with the spermatogonia, which are diploid cells - so they have 46 chromosomes, two of which are sex chromosomes, an X and a Y.
Following mitosis, a spermatogonium gives rise to two 46-chromosome daughter cells: one of them eventually becomes a primary spermatocyte, and the other one becomes a spermatogonium - this way the population of spermatogonia stays constant.
The primary spermatocyte slowly moves towards the lumen of the seminiferous tubule, passing between two Sertoli cells that nourish it.
The primary spermatocyte enters meiosis I, and emerges with 23 chromosomes each, one of which is either an X or a Y chromosome.
Secondary spermatocytes enter meiosis 2, which also have 23 chromosomes, but only one chromatid - so the right number of chromosomes and the proper amount of DNA.
It takes roughly 2 months for spermatogonia to develop into sperm, and this process is regulated by various hormones.
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